Dahlias are a huge class of flowers that have a long history of breeders, experts and aficionados. Their textual blooms with unusual petal shapes and amazing colours are amazing! Their “show flower” trait may intimidate some but they can be quite easy to grow. Given full sun, good soil and consistent water, just like a tomato plant, they thrive offering many, many blooms throughout the summer and early autumn.

Here are some general guidelines and how we treat dahlias here on our farm.

LATE WINTER/SPRING TUBER CARE
If you have received new tubers in mid Spring
Unpack & Inspect

  • Open your parcel right away.

  • Check each tuber carefully – they should feel firm (not mushy, shriveled, or mouldy).

  • A small amount of soil, dried roots, or minor surface blemishes is normal.

  • Look for “eyes” (tiny bumps or growth points) near the crown – this is where shoots will sprout.

Storage (If Not Planting Immediately)

  • In Australia, most tubers are posted out in early spring, often before it’s warm enough to plant.

  • Store tubers in a cool dry location until planting time, out of direct sun, heat or freezing temperatures.

  • Ideal: a cardboard box or paper bag with sawdust, peat moss, or wood shavings to keep them from drying out too much.

  • Do not store them in sealed plastic bags (they can rot).

  • Protecting your tubers from rodents and critters

Pre-Sprouting (Optional but Helpful)

  • About 2–4 weeks before planting, you can “wake them up” by placing them in a shallow tray with barely damp potting mix or sawdust in a bright, frost-free spot.

  • This helps you see which ones are viable and gives them a head start.

  • Dahlias, like other sun lovers, require 10-14 hours of light so as to not become leggy

PLANTING AND GROWING

TIMING
Dahlia’s are cold sensitive. Wait to plant your tubers until the ground is at least 15°C and all danger of frost has past.

SITE
Dahlias’s require full sun - at least 6 hours a day. They also benefit from late afternoon shading in areas with intense summer heat.

Choose a position with free draining, ph neutral soil. We treat our dahlia’s like tomatoes, preparing the soil in the Autumn before with well rotted manure, rock phosphate and/or bone meal depending on the soil needs. We then sow a diverse green manure mix of oats, peas, lupin, vetch, clover, rye. We leave this to grow late autumn - early spring, mowing it down and incorporating it into the soil 3-4 weeks ahead of planting our dahlia tubers.

PLANTING
Dig a hole 10-15cm deep and place the tuber on its side horizontally with the growing eye facing up. Cover with soil.

WATER
Wait to water until you see the shoot. Overwatering before you see the shoot can lead to tuber rot. We have found dahlias respond well to consistent water throughout the growing season. We use soaker hoses to achieve this. These are best laid out at planting.

Protect shoots from snails and slug.

SPACING
Some dahlias are quite large plants. We allow 36-40cm between all varieties except the pompom’s which we plant at 20cm.

PINCHING
When the shoot is about 20-30cm high, hard pinch the centre by cutting out about 10cm just above a leaf node. You should be able to see the branches forming. This encourages branching which increases flower production and stem length.

STAKING
With our farm’s proximity to the ocean, we can experience high Spring winds. We have found early staking protects young plants. That said, in our breeding project we are encouraging strong stems in hopes that with close planting, the plants will support each other. We are also cutting deep into the plants for harvest.
Corralling dahlias
We use 2.5m metal posts (pounded into the ground about 40cm) every 2.5m, a row either side of the plants. We string heavy bailing twine between each post- a new string at 20- 30cm intervals. We then just ensure that the plants are tucked into the twine on either side.

Home gardeners can secure plants to a single stake or use a metal cage system.

HARVEST AND VASE LIFE
Dahlia blooms do not keep opening after harvest. Ensure that blooms are near fully open AND check that the petals on the back side of the flower are still fresh. If they are brown, wilted and/or falling off, your vase life will be effected as the bloom is already old.

Dahlia’s are considered “event” flowers. Expect a vase life of 5-7 days with flowers cut in the coolest part of the day and placed immediately into cold water. We have great vase life results with the following three recommendations:
1) Ensure plants have been watered at least 12 hours prior to cutting.
2) Harvest in the cool part of the day and instantly hydrate the flowers.
3) Transfer to a cool shed or room.

Change the water in your container daily and/or use commercial floral preservative to keep bacteria at bay. Miniature Ball and Ball bloom types may have a longer vase life.

Flowers that will be travel benefit from one or several of the following recommendations: Transferring into buckets with 25%-50% floral preservative; Sear stem ends by placing into 70-80°C (just off boiling) water and allow to sit in water and cool for one hour; Chill for at least 8 hours at 3-4°C.

DEADHEADING
Flowers permitted to form seed shift the plants energy into seed production. This can reduce further blooms and rob energy from tuber production. Consequently we remove all blooms past their prime or damaged consistently once or twice a week.

NOTE - For more detailed information about BLOOM TYPE, please read this.

STORING DAHLIA TUBERS
To dig or not to dig - It is a question for those in mild winter areas (winters that rarely fall below 5°C) and one we cannot answer for you.  If your winter is wet and/or your ground freezes in winter, lifting your tubers protects them. Talk to other dahlia growers in your area.

We offer the following guidelines for winter storage of dahlia tubers.

  • Store your tubers in a rodent proof area or rodent proof boxes.  Mice and Rats can destroy your entire collection quickly!

  • Store in a space that maintains a temperature around 5-10C°, away from direct light.

  • Store tubers in saw dust, pine shavings or vermiculite to protect from moisture - It is a balancing act.  You want your tubers to remain plump and not dry and shrivel.  AND you want to protect your tubers from cold and rot.  If this is all new, we suggest not just putting them in a dark corner and hoping for the best.  Check on them throughout winter and see if your storage method and place of storage is working

  • Store in a space with adequate airflow to ensure condensation is not forming.

View Transition Farm Dahlia Tuber Collection

Additional Resources:
There are many online resources available.
We like books though…

Possibly more detailed then many like, we adore
DAHLIAS Seed to Bloom by Kristine Albrecht

Dahlias in Australia – The Winkie Way and was written by the late John Menzel of Winkie Dahlias is out of print but look in used book stores in case you can find this gem.

The Dahlia Society of Victoria has a comprehensive website and joining the society may offer you a great collective of growers and further learning opportunities.

Many of the US publications include photos of varieties unavailable in Australia. That is the case with Kristine Albrecht’s book BUT she has interviewed world wide growers, as did the late John Menzel, offering many different perspectives on cultivation.